The tapeworm, one of the world's least-loved creatures, is also one of the strangest. In fact, names typically used for anatomical features barely apply to tapeworms at all. For example, the barbed, bulbous appendage that this parasite sinks into the intestinal tissue of dogs and other animals, while shaped like a head, doesn't function much like one in other ways. And the individual segments of the flatworm's long, ribbon-like body are, at the same time, part of a single organism and living beings, capable of directed movement and reproduction, on their own.
Tapeworms: Ancient, Primitive and Successful
All vertebrates and many invertebrates are potential hosts to more than 5,000 identified species of tapeworm. Though these range in length from a fraction of an inch to more than 50 feet, the various species that infest dogs in North America max out at about 20 feet. Despite everything they lack -- a brain, eyes or any other sensory organs, a mouth and even a digestive tract -- tapeworms are extremely successful at what they do. Some parasites, heartworms for example, can cause the death of their hosts, thereby hastening their own demise, but tapeworms typically debilitate without killing. They absorb the nutrients from the food eaten by their hosts through their skin, generating no waste products and devoting all their energy into growing longer. Studies of gene mutations have established that the common ancestor of some species dates back as far as 1.71 million years.
You'll Seldom See the Whole Worm
The business end of the most common canine tapeworm is a globe-shaped organ bristling with hooks and suckers called the scolex or "holdfast" structure. Once the scolex is firmly attached to the dog's intestinal wall, the neckpiece starts manufacturing segments, called proglottids, each with its own muscles, nerves and reproductive system capable of fertilizing as well as generating eggs. As new proglottids are formed, those at the end of the tapeworm's tail break free and crawl towards the rectum with their cargo of eggs. These segments, about the size of a grain of rice, are likely to be the only visible evidence that a dog is infested with tapeworms. You might spot them squirming in your dog's feces or leaving his anus. As the proglottids dry out and die, they release their eggs.
Tapeworms Parasitize Other Parasites
Tapeworms require the assistance of fleas or lice to act as intermediate hosts before they can get inside a dog. If a dog is supporting a population of either of these external parasites, their larvae will be foraging in his fur, bedding and elsewhere in his environment. These larvae eat the tapeworm eggs, which hatch inside the insects' bodies but don't mature there. When the dog licks or chews at himself to ease itchiness caused by bites, he's apt to swallow some of the bugs. After they're digested, the tiny tapeworms are released into the dog's digestive system, where they attach themselves to the intestinal lining and begin generating proglottids. According to Mar Vista Animal Medical Center of Los Angeles, it only takes about three weeks from the time a dog swallows a tapeworm-infested flea to the time proglottids start to show up in his feces or around his rear end.
Creating a Tapeworm-Free Environment
If tapeworms have taken up residence inside your dog, here's the good news: These creepy parasites are killed easily with a veterinary prescription drug, administered orally or by injection, which dissolves them. In theory, humans can contract tapeworms from dogs but in practice, this rarely happens, says Cornell University's Baker Institute for Animal Health, since a person isn't likely to eat an infested flea or louse. However, because dogs and cats are both hosts for the same species of tapeworms, all animals in a household must be treated and the entire indoor environment thoroughly cleaned and decontaminated to get rid of eggs and larvae.